What causes unusual knots of gas and dust in planetary nebulas [ http://www.noao.edu/jacoby/pn_gallery.html ]? Seen previously in the Ring Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap010729.html ], the Helix [ http://antwrp.gsfc.nasa.gov/apod/ap000828.html ] Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap020512.html ], and the Eskimo Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap020407.html ], the knots' existence was not predicted previously and still not well understood. Pictured above [ http://heritage.stsci.edu/2003/06/index.html ] is a newly released image of the Dumbbell Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap030113.html ] by the Hubble Space Telescope [ http://www.stsci.edu/hst/HST_overview/ ] showing details of its gaseous knots. Also visible are many bright young stars and dark sheets of interstellar dust [ http://nedwww.ipac.caltech.edu/level5/Mathis/Mathis1.html ]. The Dumbbell Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap020302.html ], also known as M27 [ http://www.seds.org/messier/m/m027.html ], is a planetary nebula [ http://www.seds.org/messier/planetar.html ] thought similar to what our Sun [ http://www.nineplanets.org/sol.html ] will become when it runs out of core fuel for nuclear fusion [ http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fusion.html ]. Recent study [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003PASP..115..170S ] of similar cometary knots [ http://spaceimages.northwestern.edu/Cometary_Knots.html ] indicates that they include concentrations of relatively cold molecular gas [ http://antwrp.gsfc.nasa.gov/apod/ap970430.html ] and that they change significantly as the planetary nebula ages.